Re: [PATCH] mm, page_alloc: fix the duplicate save/ressave irq

[zhong jiang <zhongjiang@huawei.com>]

On 2017/3/13 19:19, Mel Gorman wrote:
> On Mon, Mar 13, 2017 at 04:02:54PM +0800, zhongjiang wrote:
>> From: zhong jiang <zhongjiang@huawei.com>
>>
>> when commit 374ad05ab64d ("mm, page_alloc: only use per-cpu allocator for irq-safe requests")
>> introduced to the mainline, free_pcppages_bulk irq_save/resave to protect
>> the IRQ context. but drain_pages_zone fails to clear away the irq. because
>> preempt_disable have take effect. so it safely remove the code.
>>
>> Fixes: 374ad05ab64d ("mm, page_alloc: only use per-cpu allocator for irq-safe requests")
>> Signed-off-by: zhong jiang <zhongjiang@huawei.com>
> It's not really a fix but is this even measurable?
>
> The reason the IRQ saving was preserved was for callers that are removing
> the CPU where it's not 100% clear if the CPU is protected from IPIs at
> the time the pcpu drain takes place. It may be ok but the changelog
> should include an indication that it has been considered and is known to
> be fine versus CPU hotplug.
>
you mean the removing cpu maybe  handle the IRQ, it will result in the incorrect pcpu->count ?

but I don't sure that dying cpu remain handle the IRQ.

Thanks
zhongjinag

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